The use of passwords to control access to resources such as computers, databases, telecommunications facilities, etc., is well known and understood. Before being given access to a requested resource, a user is required to enter a valid password as a way of ensuring that the user is authorized to access the resource. Normally, the password is a word or some other sequence of alphanumeric characters. The nodal method of entry is to speak the word into a microphone or to key the sequence of characters in on a terminal or a telephone keyboard.
Conventional alphanumeric passwords suffer from disadvantages, however. Firstly, they are difficult for the users to remember, particularly if they are arbitrary alphanumeric sequences rather than normal words. Secondly, they are relatively easy to compromise, particularly by the use of a computer that is programmed to automatically try all dictionary words or all permutations of some number of alphanumeric characters as passwords in an attempt to gain unauthorized access to a resource.
To overcome these difficulties, recently new security arrangements have been developed that rely on sensing of a user's individual and not readily duplicated characteristics as a means of validating the user's identity. These include voice analyzers, retina scanners, fingerprint image analyzers, and face image analyzers. While quite effective in overcoming the disadvantages associated with conventional alphanumeric passwords, these arrangements have disadvantages of their own. Chief amongst them is their complexity and associated cost, which make their use impractical for most of applications.